There are a number of automatic and semi-automatic rifles used by military personnel as well as law enforcement and civilians. While fully automatic rifles are generally illegal for use by the civilian population, many of the components which constitute an automatic rifle are the same as those found within semi-automatic models legalized for civilian use. Arguably the most popular semi-automatic assault-type rifle used by civilians, particularly within the United States, is the AR-15 and its clones. AR-15 is a registered trademark of Colt Industries. A number of additional companies manufacture clones of the AR-15 and market these clones under separate trademarks. While used throughout the specification, it is to be understood that the term AR-15 is meant to include not only those rifles manufactured by Colt Industries, but also those additional clones and any variants thereof. The AR-15 is the semi-automatic variant of the fully automatic M16 rifle used by United States military personnel.
The AR-15 and M16 are designed as modular rifles generally comprising a buttstock, lower receiver, upper receiver and barrel assembly. Each component is separable from one another and affords rifle owners the opportunity to customize the rifle with after-market components such as barrels of differing lengths, upper receivers designed to handle different calibers of ammunition, flashlights, hand guards, grenade or flare launchers, flash or sound suppressors, grips, and front or rear sights. To operate, the lower receiver is configured to include a trigger and magazine box wherein activation of the trigger causes a round (bullet) housed within the chamber of the upper receiver to be fired out the barrel of the rifle by action of a reciprocating bolt carrier group housed within the upper receiver. Internal mechanisms of the upper receiver expel the shell casing of the fired round from the chamber while components engaged with the magazine box housed within the lower receiver feed a new round into the now-empty chamber. The buttstock mounts to the lower receiver and includes a buffer assembly and action (or recoil) spring in communication with the bolt carrier group. After a spent shell has been discharged, the spring urges the bolt carrier group back toward the chamber in preparation for firing another round.
The modular construction of these rifles enables generally quick and easy field-stripping (disassembly of the rifle for cleaning of the rifle to ensure proper firing of the weapon). In field-stripping the rifle, the lower receiver is separated from the upper receiver to gain access to the firing mechanism (bolt, bolt carrier and associated mechanisms) for cleaning and re-lubrication. When assembled, the upper and lower receivers are secured to one another through rear and forward extensions on the upper receiver fitting between corresponding sidewalls forming notches or grooves on the lower receiver. The forward sidewalls and extension are fitted with a pivot pin to prevent the forward halves of the receivers from separating. Similarly, the rear sidewalls and extension employ a takedown pin to secure the two receivers together. To field-strip the rifle, the takedown pin is sufficiently pushed out of the extension so as to enable the rear extension to lift out of the rear sidewalls thereby pivoting the lower and upper receivers about the pivot pin. The pivot pin can then be pushed out a sufficient distance so as to enable removal of the front extension from the front sidewalls and thereby completing separation of the lower receiver from the upper receiver.
While the AR-15 and M16 can be constructed of aircraft grade forged aluminum, a trend in manufacturing current firearms/firearm components is to interchange metal parts/components with high strength polymeric materials, such as glass reinforced nylon, whenever possible. These polymeric parts/components decrease the weight of the rifle while also decreasing material costs associated with fabrication of the rifle or individual rifle parts. One drawback in polymeric components, however, is the eventual wear of these components after repeated field-stripping, cleaning and reassembly. This is of particular importance with regard to the lower receiver and the takedown and pivot pins. Any substantial wear to any of the components results in an unsafe and unusable firearm. A further drawback to a polymeric lower receiver is the potential for fatigue or cracking of the lower receiver upon dropping of the weapon. Specifically, the lower receiver includes an upper lobe which is used to mount a receiver extension (which is housed within the buttstock) to the lower receiver. The buffer assembly and action (recoil) spring is housed within this receiver extension. Dropping the rifle such that the buttstock strikes a surface with sufficient force or at an angle, or after repeated drops, the polymeric upper lobe can crack or completely fracture from the remainder of the lower receiver thereby causing misalignment between the buffer assembly and bolt carrier group resulting in a dangerous or inoperable firearm.
As such, there is a need for a lower receiver assembly which capitalizes upon the weight and cost savings afforded by polymeric materials while also enjoying the mechanical and structural strength afforded by metal (i.e. aircraft grade aluminum). The present invention addresses these and other needs.